1. Field of the Invention
The present invention relates to an apparatus for and a method of integrating switching and transferring of synchronous digital SONET/SDH signals, plesiochronous digital hierarchy PDH signals, and Ethernet signals.
2. Description of the Related Art
Generally, a synchronous optical network (SONET), a synchronous digital hierarchy (SDH) network, and a plesiochronous digital hierarchy (PDH) network use paths and bandwidths exclusively, thereby providing highly reliable and safe communications service. However, the exclusive use of the bandwidths decreases the usage efficiency of the bandwidths and the service usage price is expensive.
On the other hand, an Ethernet network that transfers Internet Protocols (IP) in frames does not use paths and bandwidths exclusively, and sharing of bandwidths is possible by using a statistical multiplexing function. Thus, the usage efficiency of the bandwidths is high and the service usage price is moderate. However, the communications reliability and safety is inferior to the SONET/SDH network because data loss through burst or runaway occurs.
Therefore, in order for a network service provider to provide a service with high reliability and safety at a moderate price in various bandwidths, both SONET/SDH network and Ethernet devices are needed. However, to operate and manage both SONET/SDH network and Ethernet devices requires high initial investment and system maintenance costs.
As a way to solve this problem, integrated systems and methods that can accept both SONET/SDH and Ethernet signals in a single platform, and switch and transfer the SONET/SDH and Ethernet signals are frequently used. These systems and methods can be classified into three categories according to a method of forming a switch fabric: forming a switching fabric with only a packet switch, forming a switching fabric with only a timeslot switch, and forming a switching fabric with a packet switch, a timeslot switch, and a signal conversion block between the packet switch and the timeslot switch.
The first method is appropriate for an application with high switching traffic among packet signals, but it has a very high difficulty in implementing a switching function for synchronous digital signals. The second method is appropriate for an application with high switching amount among synchronous digital signals, but the cost of a packet exchange service increases a lot compared to the first method. The third method can form a system accordingly to a switching amount among packet signals and synchronous digital signals, and can provide a conventional packet exchange service and a synchronous timeslot exchange service with the same quality and price.
Another method besides the previously mentioned ones is to use an asynchronous transfer mode (ATM) switch and to switch synchronous digital signals and packet signals after they are transformed into ATM cells. This method has an advantage of providing a reliable virtual connection service by the ATM. However, to apply this method, an additional connection setting is required even for sending the packet signals, which makes it difficult to control an application. Also, it is difficult to apply this method to a large-capacity system since the complexity of the method increases as the system capacity increases.